Mucus secretion is a normal function of respiratory mucous membranes. Models for measurement of mucus production by cultured human and feline bronchial and nasal mucosae have been developed in order to examine the controls of mucus secretion. In addition to neurohormones and mediators of allergy, airways react to products generated by pulmonary macrophages and peripheral mononuclear cells with increased mucous glycoprotein secretion. The macrophage and mononuclear derived secretagogues are collectively being called macrophage/mononuclear cell derived mucus secretagogues (MMS). Corticosteroids inhibit MGP release by lowering baseline secretion. Analysis of corticosteroid treatment airways reveals a close correlation between lipocortin generation and MGP production. Pulmonary inflammation with neutrophils is often associated with mucus production. Lysates of human neutrophils as well as supernatants from activated neutrophils cause airways to release MGP; this activity is not due to elastase, and identity of the mucus secretagogue is under study. Endorphins cause increased MGP secretion. Substance P is found in close association with submucous glands. Substance P causes MGP secretion and the activity of substance P is markedly increased by protection from degradation by proteases with thiorphan.